Fuel cell systems have been proposed as power sources for a varying number of applications, including mobile, vehicular applications. Generally, the fuel cell system includes a fuel cell stack that uses hydrogen to produce an electrical current for powering an external device. The hydrogen may be supplied to the fuel cell stack directly from a hydrogen source. An alternative to hydrogen storage onboard a vehicle is reformate generated from a hydrocarbon fuel. To this end, an auto-thermal reformer is implemented for reforming the hydrocarbon fuel to produce a reformate stream having a hydrogen component. Reformation of the fuel within the auto-thermal reformer requires a mixture of fuel and water in a gaseous state (i.e. vaporized fuel and steam). To achieve the gaseous state, heat transfer (or surface-type) vaporizers are provided immediately prior to the auto-thermal reformer for vaporizing the water and in some cases the fuel.
Typical surface-type vaporizers function by pooling fluid on or around a heat transfer surface. Pooling of fluid, however, entails an aggregation of fluid resulting in a slow transient response between pool formation and vaporization. Fuel cell applications, in particular vehicular applications, are characterized by transient power requirements for acceleration. These transient power demands require fast fluid vaporization for supplying vaporized liquids to reaction vessels for reforming the hydrocarbon fuel.
One means of overcoming this problem is to employ volume, or direct spray vaporizers. Such devices, however, are cumbersome and require high grade heat, leading to reduced system thermal efficiency.
Therefore, it is desirable in the industry to provide an improved surface-type vaporizer and vaporization method overcoming the disadvantages associated with traditional surface-type vaporizers. In particular, the improved vaporizer should decrease the transient response time for fluid vaporization for meeting system power demands.